Kinases, also known as phosphotransferases, are enzymes that transfer phosphate groups from high energy donor molecules (ATP) to specific target molecules (substrates). Kinases are involved in a variety of cellular processes including cell signaling. Certain cellular signaling processes have been implicated as important in a number of medical conditions and the effective inhibition of certain cell signaling processes, therefore they may provide the potential to stop these conditions from developing or treating medical conditions where such processes are up regulated or uncontrolled. Accordingly, kinases represent an attractive target and kinase inhibitors potentially affect signaling processes to be controlled leading to the control or treatment of certain medical conditions.
The phosphoinositide 3-kinase (PI3) family of kinases are a family of kinases which are involved in a wide range of cellular events such as cell migration, cell proliferation, oncogenic transformation, cell survival, signal transduction and intracellular trafficking of proteins, and have recently been the focus of much research aimed at developing therapies for a range of proliferative diseases, for example cancer, immune and inflammatory diseases, diseases supported by excessive neovascularization and transplant rejection.
The phosphoinositide 3-kinase (PI3K) family is a group of enzymes that generate lipids such as phosphatidylinositol. These lipids are involved in a wide range of physiological processes. In mammalian cells, the large PI3K family has been categorized into three classes, I, II, and III (Stephens et al., Curro Opin. Pharmacol. 2005, 5, 357). Class I PI3K convert phosphatidylinositol-4,5 bisphosphate (PIP2) to phosphatidylinositol-3,4,5 trisphosphate (PIP3). Class I PI3Ks are further comprised of Class IA and 1B PI3 kinases (PI3Ks).
Class I PI3Ks are key players of multiple intracellular signaling networks that integrate a variety of signals initiated by many growth factors. The Class IA enzymes are activated by tyrosine kinases (e.g. growth factor receptors), antigen receptors, and cytokine receptors, whilst the Class IB enzyme is activated by ‘G Protein Coupled Receptors’ (GPCRs). In response to activation, the PI3Ks generate lipid second messengers, which bind to, and activate, specific proteins in distinct signal transduction pathways. The signal transduction pathways remain active until phosphatase enzymes, in particular the oncogene PTEN, dephosphorylate the PI3K lipid second messengers. The PI3K signaling pathway is crucial to many aspects of cell growth and survival via its regulation of widely divergent physiological processes that include cell cycle progression, differentiation, transcription, translation and apoptosis. Constitutive activation of the PI3K pathway has been implicated in both the pathogenesis and progression of a large variety of cancers and there is now a body of evidence that demonstrates conclusively that PI3K signaling is frequently dysregulated in cancer.
A signaling pathway mediated by the PI3 kinases is the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which is critically involved in the mediation of cell survival and is a major signaling component downstream of growth factor receptor tyrosine kinases (RTKs). The PI3K-Akt signaling pathway regulates many cellular processes including cell proliferation, survival, growth, and motility-processes that are critical for tumorogenesis. The role of the PI3K/Akt pathway in oncogenesis has also been extensively investigated and mutations or altered expression of most of the pathway's components have been widely implicated in many cancers. Through a variety of mechanisms, many human cancers possess activated PI3K signaling.
These data provide strong validation for the development of novel anticancer strategies using inhibitors of PI3Ks. Interest in PI3K inhibitors has been intense with a number of compounds now in development having demonstrated anti-tumor activity in animal models. Compounds are also undergoing evaluation in clinical trials.
Since, PI3-kinase isoforms regulate different aspects of immune and inflammatory responses, there is great interest in the role of PI3-kinase signaling in a range of immune and inflammatory diseases as well as in transplant rejection.
PI3K isoforms also play a key role in the downstream signaling pathways of angiogenic growth factors such as VEGF, FGF and PDGF as well angiogenic cytokines. mTOR, another downstream serine/threonine kinase, is involved in the regulation of vascular endothelial growth factor (VEGF), hence PI3K and mTOR inhibitors also have potential to treat diseases supported by pathological neovascularization such as during tumorogenesis, inflammatory conditions such as rheumatoid arthritis and ocular neovascular diseases, e.g. age-related macular degeneration (AMD), retinal vascular diseases (vein occlusion and diabetic retinopathy) and other possible proliferative vascular disorders.
The p110 alpha isoform is selectively amplified and activated in a number of cancer types (Stephens et al., Curr. Opin. Pharmacol. 2005, 5, 357; Stauffer et al., Curr. Med. Chem.-Anti-Cancer Agents 2005, 5, 449). In addition, there is a high frequency of nonrandom mutations in specific sites, primarily in the C2 domain and or the activation loop, of the kinase in several human cancer cell lines, including colon, brain, breast, and stomach (Samuels et al., Science 2004, 304, 554). This results in a constitutively active enzyme (Ikenoue et al., Cancer Res. 2005, 65, 4562; Kang et al., Proc. Natl. Acad. Sci. USA 2005, 102, 802), making p110□ one of the most highly mutated oncogenes found in human tumors. Structural studies have shown that many of the mutations occur at residues lying at the interfaces between p110□ and p85□ or between the kinase domain of p110□ and other domains within the catalytic subunit (Miled et al., Science 2007, 317, 239; Huang et al., Science 2007, 318, 1744).
While PI3K isoenzymes play important roles in many cellular processes, published experimental studies in mice with human tumor xenografts show that the pan PI3K inhibitor LY294002 is well-tolerated, reduces signaling through the PI3K pathway, causes reduction of tumor volume, and is more active in cell lines over-expressing mutant forms than parental control cells (Semba et al., Clin. Cancer Res. 2002, 8, 1957; Hu et al., Cancer Res. 2002, 62, 1087).
Thus, PI3K, is an interesting target for drug intervention. Several classes of compounds have been identified as reversible inhibitors; for example, LY 294002 (Walker et al., Mot Cell. 2000, 6, 909), PI103 (Knight et al., Cell 2006, 125, 733; Hayakawa et al., Bioorg, Med. Chem. Lett. 2007, 17, 2438; Raynaud et al., Cancer Res. 2007, 67, 5840), ZSTK474 (Yaguchi et al., J. Natl. Cancer Inst. 2006, 98, 545; Kong et al., Cancer Sci. 2007, 98, 1639), TGX221 (Jackson et al., Nat. Med. 2005, 11, 507), oxazines (Lanni et al., Bioorg. Med. Chem. Lett. 2007, 17, 756), IC87114 (Sadhu et al. WO 2001/81346; Billottet et al., Oncogene 2006, 25, 6648), AS605240 (Camps et al., Nat. Med. 2005, 11, 936), the imidazo[1,2-a]pyridines (Hayakawa et al., Bioorg. Med. Chem. 2007, 15, 403; Hayakawa et al., Bioorg. Med. Chem. 2007, 15, 5837), and the imidazo[4,5-c]quinoline NVP-BEZ235 (Garcia-Echeverria, et al., WO 2006/122806).

All of the above mentioned compounds function as reversible inhibitors of the appropriate PI3K isoforms. Although irreversible activity is displayed by the fungal metabolite wortmannin and its analogues, such as PWT-458 (Zhu et al, J. Med. Chem., 2006, 49, 1373) and PX-866 (Wipf et al., Org. Biomol. Chem. 2004, 2, 1911; Zask et al., J. Med. Chem. 2008, 51, 1319), these compounds are not selective for individual PI3K isoforms, undergoing reaction with a conserved lysine amino group (e.g., Lys-802 in P110□, Lys-805 in P110□, Lys-833 in P110y, and Lys-799 in P110□).
Despite the advances in developing PI3K inhibitors, there is an unmet need for PI3K inhibitors that are more potent and more selective, exhibit better pharmacokinetic properties, and/or produce fewer side effects than the existing PI3K inhibitors.